feat(deprecation): remove safetyCritical retention multiplier and type-cap bypass

- Remove SAFETY_CRITICAL_FACTOR = 6.0 from workspace-memory.ts
- Remove safetyFactor from calculateInitialStrength() - all memories now
  fade according to the same rules
- Remove safetyCritical bypass from applyTypeMaxCaps() - safetyCritical
  entries compete normally under TYPE_MAX caps
- Preserve safetyCritical?: boolean in LongTermMemoryEntry type for
  backward compatibility (no producer sets it to true)
- Update memory-diag to show deprecation warning instead of capacity alert
- Update tests: add backward-compatibility fixture test, deprecation
  strength test, normal cap competition test
- Update docs/architecture.md, RELEASE_NOTES.md, CHANGELOG.md,
  docs/configuration.md

Phase 1.5 complete: safetyCritical is now a deprecated field with no
active behavior. Safety rules belong in user-controlled agent.md files.

src/workspace-memory.ts

@@ -40,8 +40,6 @@ const USER_IMPORTANCE_FACTOR = {
   high: 1.5,
 } as const;
 
-const SAFETY_CRITICAL_FACTOR = 6.0;
-
 const TYPE_MAX = {
   feedback: 10,
   decision: 10,
@@ -53,9 +51,8 @@ export function calculateInitialStrength(memory: LongTermMemoryEntry): number {
   const typeFactor = TYPE_FACTOR[memory.type] ?? 1.0;
   const sourceFactor = SOURCE_FACTOR[memory.source] ?? 1.0;
   const importanceFactor = USER_IMPORTANCE_FACTOR[memory.userImportance ?? "normal"] ?? 1.0;
-  const safetyFactor = memory.safetyCritical ? SAFETY_CRITICAL_FACTOR : 1.0;
 
-  return typeFactor * sourceFactor * importanceFactor * safetyFactor;
+  return typeFactor * sourceFactor * importanceFactor;
 }
 
 export function calculateEffectiveHalfLife(memory: LongTermMemoryEntry): number {
@@ -660,11 +657,6 @@ function applyTypeMaxCaps(entries: LongTermMemoryEntry[]): LongTermMemoryEntry[]
   const typeCounts: Partial<Record<LongTermMemoryEntry["type"], number>> = {};
 
   for (const entry of entries) {
-    if (entry.safetyCritical) {
-      capped.push(entry);
-      continue;
-    }
-
     const count = typeCounts[entry.type] ?? 0;
     const max = TYPE_MAX[entry.type] ?? Infinity;
     if (count >= max) continue;